FactCheck: how green is my Prius?

The FactCheck Green series takes a look at that icon of 'enivronmentally concious' driving: the Toyota Prius.

Background

Any celebrity with a conscience has one: Tom Hanks, Leonardo DiCaprio, Cameron Diaz, even Kevin Bacon have all got on board.

Arnold Schwarzenegger has even given their drivers tax breaks - although he still prefers to stick with his old gas-guzzling Hummer.

Yes, the Prius has become the ride of choice for the environmentally conscious Hollywood star.

With its combination of electric and petrol engines, Toyota's flagship hybrid car is meant to be a much more efficient way to drive, particularly within urban areas - producing less pollution and making less of a contribution to global warming.

Sales are still small by auto industry standards, but growing fast; Toyota expects to sell 8,500 in the UK this year, up from 5,017 the year before. Worldwide, the company sold 118,123 in the first five months of this year.

But is it actually greener? The Prius's status as a green motoring icon depends very much on whether it really is less environmentally damaging than other cars. And some reports suggest it isn't.

Analysis

The status of the Prius was recently challenged by a UK government report - compiled in association with What Car? Magazine - which ranked UK cars by fuel efficiency.

The Prius did pretty well, producing just 104 grams of carbon dioxide for every kilometre travelled, compared to 283g for a top-of-the-range sports car.

But at just 99 g/km the humble Volkswagen Polo Blue Motion Diesel pips it at the post.

It was a result that delighted eco-iconoclasts, prompting many claims that the Prius's eco-crown had slipped. But this in itself is not enough to destroy the Prius's green credentials.

Emissions from driving don't represent the total environmental impact across the lifetime of a car.

Carbon dioxide emissions are only one aspect of the car's environmental appeal.

Diesel engines produce relatively large amounts of other pollutants, such as nitrogen oxides and particulates, which are a particular problem in cities.

Electric engines are also much more efficient for urban driving, which involves lots of stopping and starting at traffic lights.

However, emissions from driving don't represent the total environmental impact across the lifetime of a car.

The result of this survey was rather skewed by some of the assumptions made when they prepared the report.

A US research company has made an attempt to analyse the carbon dioxide emissions from the Prius over its lifetime, from the mining of raw materials to the eventual destruction of the used car.

They came up with an even more eye-catching line: a Prius is even more damaging than the vast, gas-guzzling Hummer - the very symbol of wasteful driving.

However, the result of this survey was rather skewed by some of the assumptions made when they prepared the report. For one thing, it uses a rather low estimate of the number of miles a Prius will be driven during its lifetime - 109,000, just over half the figure it uses for the Hummer.

It also uses very high estimates of the impact of producing and designing a vehicle versus driving it.

Most estimates reckon that fuel burnt while driving accounts for about 80 per cent of a car's lifetime carbon dioxide impact. For the Prius in the CNW study, it's just two per cent - absurdly low.

Even taking all these things into account, the Prius still beats the Hummer hands down.

The Prius is a complex, highly engineered vehicle using new technology, so its production and development costs will be high.

It still sells in relatively low numbers - so those research and development costs are averaged out across a large number of vehicles.

But even taking all these things into account, the Prius still beats the Hummer hands down.

The Rocky Mountain Institute did a more orthodox lifecycle analysis of the two cars side by side, and even taking the more extreme of the CNW assumptions on board, the Prius beat the Hummer every time.

Other studies have given the Prius very good marks - the American Council of an Energy Efficient Economy's Greenercars.org rankings have it down as the greenest car available - but this is in the US, so all cars in the list are automatics, which are less efficient than manual transmission cars.

Verdict

The Prius is clearly a very efficient car. Whether it is absolutely the most efficient of all is probably less important.

The CNW report certainly doesn't undermine the environmental case for driving small hybrid cars. It may well be more costly to build than simple diesels, and the research and development costs may be greater, but that in turn holds out the hope for even more efficient vehicles in the future.

The mark 2 Prius represented a 13 per cent improvement over the mark 1 version - and future hybrids and other electric vehicles from Toyota or other manufacturers should provide even greater efficiencies in the future.

But in any case, the benefits of driving them aren't just their overall energy efficiency. The electric drive produces far lower energy emissions when driving around cities; low-speed, stop-start driving is where petrol and diesel cars are least efficient, and produce the most noxious gases.

FactCheck rating: 2

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